"Didn’t I say it was an Erumpent horn, didn’t I tell him? And now his house has been blown apart!”
-- Hermione Granger (DH22)
A glowing fluid from the horn of an Erumpent. An Erumpent can fill something with this fluid by piercing it with its horn. Soon after that, the item will explode (WFT).
References from the canon
Newt Scamander's escaped Erumpent blew up a tree in Central Park (WFT).